Sub Test()
Dim LastRow As Long, i As Long
    
    Application.ScreenUpdating = False
    With ActiveSheet
        LastRow = .Cells(.Rows.Count, 1).End(xlUp).Row
        For i = 2 To LastRow
            If Not IsEmpty(.Cells(i, 2)) Then .Cells(i, 1) = .Cells(i, 2)
        Next i
    End With
    Application.ScreenUpdating = True
    MsgBox "Данные в столбце А заменены!", vbInformation, "Конец"
End Sub